Bottom antireflection coating color filter process for fabricating solid state image sensors
View Patent ↗An image sensor system and methods of making such a system are described. The image sensor system includes a color filter array that is formed by a color filter process that incorporates a bottom antireflection coating. The bottom antireflection coating forms a protective layer that protects exposed areas of the active image sensing device structure during formation of the color filter array and, thereby, preserves the intrinsic transmission characteristics of the active image sensing device structure. The bottom antireflection coating also reduces degradation of metal structures (e.g., bonding pads) and pixel edges at the exposed surface of the active image sensing device structure. In addition, the bottom antireflection coating provides a reliable adhesive surface for the color filter array, substantially eliminating lifting of the color filter array resist structures. In some embodiments, the bottom antireflection coating also improves the optical transmission characteristics of one or more colors of the colors filter array.
1. A method of fabricating an image sensor, comprising:
forming a bottom antireflection coating over an exposed surface of an active image sensing device structure;
forming a color filter array on the bottom antireflection coating; and
substantially removing exposed portions of the bottom antireflection coating;
wherein
the active image sensing device structure comprises an array of light sensing elements,
forming the color filter array comprises forming an array of color filters each disposed over a respective light sensing element such that light travels from each color filter to a respective light sensing element through a respective light transmission path substantially transmissive to radiation in a visible wavelength range,
forming the bottom antireflection coating comprises forming the bottom antireflection coating with a thickness less than approximately 200 nm, and
after the removing, remaining portions of the antireflection coating are disposed in each light transmission path between the color filter array and the active image sensing device structure.
2. The method of claim 1 , wherein the bottom antireflection coating comprises a dyed organic film-forming material.
3. The method of claim 1 , wherein the bottom antireflection coating comprises a light-absorbing polymeric film-forming material.
4. The method of claim 1 , wherein the bottom antireflection coating is substantially transmissive to radiation in a wavelength range of about 400 nm to about 700 nm.
5. The method of claim 1 , wherein the color filter array comprises a plurality of colored photoresist structures.
6. The method of claim 1 , wherein exposed portions of the bottom antireflection coating are removed substantially by a plasma etch process.
7. The method of claim 6 , wherein the plasma etch process is a low-power buffered oxygen ash process.
8. The method of claim 1 , wherein the bottom antireflection coating forms a substantially continuous layer over the exposed surface of the active image sensing device structure before exposed portions of the bottom antireflection coating are substantially removed.
9. The method of claim 1 , wherein the bottom antireflection coating forms a protective barrier over metal structures at the exposed surface of the active image sensing device structure during formation of the color filter array.
10. The method of claim 1 , wherein the active image sensor device structure comprises a complementary metal-oxide-semiconductor (CMOS) image sensor.
11. A method of fabricating an image sensor, comprising:
forming a bottom antireflection coating over an exposed surface of an active image sensing device structure:
forming a color filter array on the bottom antireflection coating; and
substantially removing exposed portions of the bottom antireflection coating;
wherein the bottom antireflection coating has a thickness selected to improve an optical transmission characteristic of one or more colors of the color filter array.
12. A method of fabricating an image sensor, comprising:
forming a bottom antireflection coating over an exposed surface of an active image sensing device structure;
forming a color filter array on the bottom antireflection coating; and
substantially removing exposed portions of the bottom antireflection coating, wherein exposed portions of the bottom antireflection coating are removed substantially by a plasma etch process that removes the bottom antireflection coating at a substantially higher etch rate than the color filter array.
13. A method of fabricating an image sensor, comprising:
forming a bottom antireflection coating over an exposed surface of an active image sensing device structure;
forming a color filter array on the bottom antireflection coating; and
substantially removing exposed portions of the bottom antireflection coating, wherein, after the removing, the bottom antireflection coating is present only in regions directly under color filter array material.
14. A method of fabricating an image sensor, comprising:
forming a bottom antireflection coating over an exposed surface of an active image sensing device structure, wherein the bottom antireflection coating has a thickness of about 60 nm;
forming a color filter array on the bottom antireflection coating; and
substantially removing exposed portions of the bottom antireflection coating.